BNE- after passport control go left andfollow the signs to the Qantas Club (International Business Lounge) / Lounges. Go up the escalator and at the Qantas desk, they will point you to your left, where a frosted panel will slide open. Presto, you are then able to enter the small Flounge area.
SIN - come out of passport control and turn left, follow the signs to the Qantas Lounges, go up the escalator and continue forward. You will then see the First lounge (well signed) directly ahead (and will pass the Qantas Club/International Business Lounge on your left).